[Click] How to reference Method Interfaces?

[刘冰洋]

Hi~, I'm a fresh man for click.
I learned "Flow-Based Router Context", and it is said that "A can refer to B
by name". But I couldn't find any tutorial about "Refer Element's Method
Interface by Name".
For example, there is a configuration:
    ... -> q::Queue -> MyPrint(config string) -> ...
    MyPrint() is just an element which passes packets unchanged, and will
print any type of data as configured.
    and i want to print q's length().
    How can I achieve that?
Thx!!

-- 
Bjorn Liu
Tsinghua Uni, Beijing, China
+86 010 51531429
+86 13141300043